Is there an easy way to see the number of houses?
It is in the Town Hall Overview tab.
So all you have to do is build a Town-Hall and select it, it'll display the number of Houses (marked as "Homes" in the image linked below) along with some other helpful information.
As far as occupancy, you get a rough estimate by looking at the number of families vs the number of homes. Generally speaking there's a 1:1 ratio.
Source: http://banished.gamepedia.com/File:Town_hall_overview.png